Bituminous compositions for use in roofing materials such as roll roofing products are known in the art. It is desirable to use styrene-butadiene-styrene (SBS) block copolymer-modified asphalt in the manufacture of shingles for many of the same reasons that SBS modified roll roofing products are desirable. They have improved wind resistance, impact resistance, and tear resistance. They are more resistant to cracking at low temperature. They are more flexible, so they are less susceptible to long term damage from thermal cycling.
There are added challenges in the manufacture of SBS modified shingles above and beyond the normal challenges experienced in the manufacture of SBS modified roll roofing products. In order to achieve suitable slump resistance, suitable fire resistance, and moderate raw material costs, shingle asphalt formulations contain 60% or more filler, where flame retardants may replace part of the filler. At these high filler loadings, the viscosity of the asphalt increases rapidly.
Conventional shingles are manufactured on high speed lines running up to 600 feet per minute. They typically consist of an organic or fiberglass felt coated with oxidized asphalt which contains a high loading of filler. In order to have sufficiently low viscosity to run at high speeds, shingle lines typically operate at higher temperatures than roll roofing lines, typically greater than 400.degree. F. Modification of asphalt with conventional SBS polymers causes a very large increase in viscosity. This high viscosity combined with the viscosity increase from the filler content makes SBS modified asphalt extremely difficult to process in shingle applications. Thus it is desirable to have SBS modified asphalt formulations which maintain suitable physical properties in the final product but have reduced viscosity to facilitate processing.